Numerical Simulations of Flow Patterns in Crossflow Rotary Devices*

Crossflow rotary devices, including both Darrius-type turbines and cyclorotors used for propulsion, have been widely proposed for application in aquatic contexts. Increasing understanding of the negative effects of anthropogenic acoustic noise on aquatic ecosystems has driven interest in numerically predicting radiated noise from marine devices. To date, most of the regulatory and research efforts have focussed on the effects of conventional marine propellers, while crossflow devices remain relatively unexplored. In turbomachinery applications, the primary sources of noise are shed vorticity and cavitation, when it occurs. Predicting radiated noise from vortices and cavitation requires an accurate solution of the shed vorticity in the wake and the resulting fluctuating pressure. In this study, we show that the flow patterns inside the crossflow rotor is a primary determinant of fluctuating pressure. We present a set of CFD simulations spanning advance ratios from 0.6 to 3.6. The solutions of the unsteady Reynolds-averaged Navier-Stokes (URANS) equations suggest that the production of noise cannot reliably be predicted by the operational speed or flow-through rate of the device and is instead dependant on vortex-blade interactions.